# 16.11.2023 [1980. Find Unique Binary String]

First absent number in a binary string array

16.11.2023

1980. Find Unique Binary String medium
blog post

Join me on Telegram

https://t.me/leetcode_daily_unstoppable/406

Problem TLDR

First absent number in a binary string array

Intuition

The naive solution would be to search in all the numbers 0..2^n. However, if we convert strings to ints and sort them, we can do a linear scan to detect first absent.

Approach

• use padStart to convert back

Complexity

• Time complexity:
  O(nlog(n))

• Space complexity:
  O(n)

Code

    fun findDifferentBinaryString(nums: Array<String>): String {
      var next = 0
      for (x in nums.sorted()) {
        if (x.toInt(2) > next) break
        next++
      }
      return next.toString(2).padStart(nums[0].length, '0')
    }